Ignition system



April 23, 1968 A. D. RITTMANN ET AL 3,379,182

' IGNITION SYSTEM I Filed April 29, 1966' 44 M E l 130 0 v I ll WNW/ 3/ if! I Q Q Q I4 1 v INVENTORf? ALBERT D. HITTNANN JANES E. SHEARER HIS ATTORNEY (w Agra: v a 1,, f If; m brats at 3,379,182 EGNITHQN SYSTEM Aibert i). Rittmann and James E. Shearer, Kokomo, Ind., assignors to General Motors Corporation, Detroit, Mich, a corporation of Delaware Filed Apr, 29, 1966, Ser. No. 546,300 3 Claims, (Cl. 123-148) AETRAUBT OF THE DISCLOSURE An ignition breaker point operated transistorized ignition system which utilizes a transistor switch for establishing and interrupting the energizing circuit for the primary winding of the ignition coil and an inductor device for extiguishing the transistor upon the opening of the breaker points wherein the combination of a resistor connected in parallel with the breaker points for rendering the transistor switch reconductive before the points recluse and a diode connected in serie with the The present invention relates to ignition systems for internal combustion engines and, more specifically, to an ignition system employing a semiconductor switching device which may be used with conventional ignition breaker points operated by a lobed cam.

With any ignition system for internal combustion engines, it is desirable to provide for a high build-up of energizing current through the primary winding of the ignition coil prior to each subsequent spark and with ignition systems in which a semiconductor device is employed as the ignition coil primary winding switch, it is desirable to include a feature which will automatically limit the current fiow through the current carrying electrodes of this device.

Heretofore, quite complex electronic circuitry has been devised to realize these two desirable features. As elec tronic circuitry and Components are expensive and since the use of semiconductor switching devices is becoming increasingly popular, the requirement of a simple, inex- I pensive ignition system which provides the two desirable features hereinabove set forth, is apparent.

it is, therefore, an object of this invention to provide an improved ignition system.

it is another object of this invention to provide an improved ignition system employing a semiconductor switching device;

It. is another object of this invention to provide an improved ignition system employing a semiconductor switching device for use with conventional igniti'on breaker points which provides a greater build-up of energizing current through the primary winding of the ignition coil than is obtainable by the opening and closing of the breaker points,

It is an additional object of this invention to provide an improved ignition system which includes a feature for automatically limiting the current flow through a semiconductor device employed as the ignition coil primary winding energizing and de-energizing switch.

in accordanc with this invention, an improved ignition system for use with conventional ignition breaker points is provided wherein the maximum current flow through a semiconductor device, employed as the energizing switch for the primary winding of the ignition coil, is automatically limited to a safe, predetermined value and the period during which the semiconductor device remains nonconductive after the ignition breaker points open is of a period of time less than that required to close the ignition breaker points.

Fora better understanding of the present invention, together with additional objects, advantages and features thereof, reference is made to the following descriptionza'nd accompanying single figure drawing.

Referring to the figure, the ignition system of this invention is set forth in schematic form in combination with a pair of conventional ignition circuit breaker points 10 and 11 which are opened and closed by a lobed cam 12 which is driven by engine 14 and engages cam follower 15, in a manner well known in the automotive art.

The primary winding 16 of a conventional ignition coil 18 is connected in series across a source of direct current potential, which may be a conventional storage battery 21, through a conventional electric switch 22 having a movable contact 23 and two stationary contacts 24 and 25, the current carrying electrodes of a semiconductor switching device 30, a resistor 36 and point of reference or ground potential 5which, since it is the same point electrically, has been referenced by this same numeral throughout the figure.

Switch 22 may be a conventional automotive type ignition switch having an off positon, as shown in the figure, a crank position with movable contact 23 closed to stationary contacts 24 and 25 and a run position with movable contact 23 closed to only stationary contact 25. Switches of this type are well known in the art and are normally spring biased to return to the run position upon the release of pressure upon the ignition key,

Without intention or inference of a limitation thereto, the semiconductor switching device may be a type NPN transistor having the usual current carrying electrodes, collector electrode 31 and emitter electrode .32, and a control electrode, base electrode 33, as schematically set forth,

With movable contact 23 of switch 22 closed to either or both stationary contacts; the current carrying electrodes, collector electrode 31 and emitter electrode 32, of switching transistor 30 are connected in series with primary winding 16 of ignition coil 18 across the source of direct current potential, battery 21, through resistor 36 and point of reference or ground potential 5.

As the collector electrode 31 and emitter electrode 32 of transistor switch 30 are connected to the positive and negative polarity terminals, respectively, of battery 21 through movable contact 23 of switch 22 closed to either or both of the stationary contacts and point of reference potential 5, respectively, this device is forward poled, The control or base electrode 33 of transistor 30 is connected to junction 34 between resistor 35 and the series combination of diodes 38 and 40, The impedance values of diodes 38 and 40 and resistor 35 are arranged to provide a potential at junction 34 which is of a positive polarity in respect to the potential present upon the emitter electrode 32 of transistor 30. As this is the proper potential polarity relationship to produce base-emitter current flow through a type N'PN transistor, transistor 30 is normally conducting with the circuit energized.

To quickly extinguish or render transistor 30 nonconductive in response to each opening of ignition breaker points 10 and 11, an inductor device 42, connected in shunt across the base electrode 33 of transistor 30 through resistors 35 and 41 and point of reference potential 5, is provided,

To provide for a maximum build-up of energizing current through the primary winding 16 of ignition coil 18, it is necessary that the dwell time or the period of time during which transistor switch 30 is conducting be as long as possiblc. To realize the highly desirable long dwell time, it is mandatory that transistor switch 30 be nonconductive for the shortest possible time consistent with the establishment of a spark. To provide for the triggering of transistor switch 30 conductive even before the closure of ignition breaker points 10 and 11, a resistor 44, connected between line 17 and the base electrode 33 of transistor switch 30, is provided.

As transistor 30 is first made conductive by resistor 44, a condition of oscillation persists in ignition coil 18 as a result of its distributed capacitance, its inductance and a certain amount of retained energy from the previous spark. Diode 45 is provided to prevent this oscillatory energy from establishing current of the undesirable direction in primary winding 16 of ignition coil 18, thereby effectively increasing the build-up of energizing current in the desirable direction.

To provide the current limiting feature which limits the maximum amount of collector-emitter current flow through transistor switch 30, the series combination of diodes 38 and 40 is connected in parallel with the series combination of emitter electrode 32 of transistor switch 30 and resistor 36 between junction 34 and point of ref ercnce or ground potential 5.

In operation, switch 22 is operated to the crank position at which time movable contact 23 is closed to stationary contacts 24 and 25 to energize the system. With ignition breaker points 10 and 11 closed, transistor switch 30 is conducting and energizing current flows through pri mary windirr; 16 of ignition coil 18 from battery 21, through a circuit which includes closed switch 22, primary winding 16, the collector-emitter electrodes of transistor switch 30, resistor 36 and point of reference potential 5. As a cranking motor, not shown, begins to rotate engine 14 in a manner well known in the art, a lobe of cam 12 engages cam follower l and opens ignition breaker points Ill and 11. As this arrangement is well known in the automotive art and forms no part of this invention, in the interest of reducing drawing complexity, the the cranking motor has not been shown in the figure.

As breaker points and 11 open, the potential appearing across inductor 42 is reduced in magnitude and the resulting collapsing magnetic field induces a potential therein which is of a negative polarity at junction 34 in respect to point of reference or ground potential 5. As

this potential, applied across the base-emitter electrodes of transistor switch 30, is of the incorrect polarity relationship to maintain base-emitter current flow through a type NPN transistor, this device is immediately extinguished. With transistor switch 30 in the nonconductive mode, the energizing circuit through which current is supplied to primary winding 16 of ignition coil 18, is interrupted and the resulting collapsing magnetic field induces a high potential in secondary winding thereof which appears across terminal 46 and point of reference potential 5. As is well known in the automotive art, this high potential is directed by a conventional automotive type distributor, not shown, to the proper spark plug of engine 14. As this arrangement is well known in the automotive art and forms no part of this invention, it has not been shown in the figure.

Simultaneously with the decay of the induced potential appearing across inductor 42, current flow through resister 44 and the base-emitter electrodes of transistor switch triggers transistor switch 30 conductive. With the inclusion of resistor 44 in this unique circuit, transistor switch 30 is rendered conductive before the ignition breaker points 10 and 11 rcclose as the lobe of cam 12 passes cam follower 15. With this novel feature, the dwell time of this unique ignition system may be considerably lengthened in that the energizing circuit for primary winding .16 of ignition coil 18 is closed faster than would be possible with only the conventional ignition:

transistor 30 is first rendered conductive by current flow through resistor 44 and the base-emitter electrodes thereof, there persists, from the previous spark, a certain amount of energy retained in the inductance and distributed capacitance of ignition coil lll. Due to the bidirectional current conduction capabiiity of transistor 30, this retained energy tends, for a short time, to establish an oscillatory current through battery 21, primary winding 16 of ignition coil 18 and transistor 30. Diode 45 prevents current from flowing in a direction opposite to that induced by the battery. In so doing, the diode 45 allows a greater realization of the transistor conduction time in the accomplishment of a high energizing current in the primary winding 16 of ignition c0il.18 prior to the next spark.

From this description, it is apparent that resistor 44, by rendering transistor 30 conductive before breaker points 10 and 11 open, and diode 45, by preventing oscillatory currents in the undesirable direction through primary winding 16 of ignition coil 18, each independently provided for a greater buildup of energizing current through primary winding 16 prior to each subsequent spark. It is to be specifically understood, however, that the novel circuit of this invention is not to be construed as limited only to this combination as each may be employed separately to provide for increased primary winding 16 energizing current.

With energizing current'flowing through primary winding 16 of ignition coil 18 and the collector-emitter electrodes of transistor switch 30, a potential'drop, which increases in magnitude with an increase in energizing current, appears across resistor 36. When the magnitude of this potential drop reaches a magnitude substantially equal to the potential drop across one of diodes 38 or 40 with an increase of collector-emitter current how, the baseemitter junction of transistor switch 30 becomes less forward biased and, as a result, base electrode current is diverted through conducting series-connected diodes 38 and 40. With base current flow diverted through these diodes, transistor switch 30 is taken out of saturation, a condition which limits the amount of current flowing therethrough.

With this arrangement, therefore, and by carefully s selecting the value of resistor 36 relative to the potential drop across one of seriesconnected diodes 38 and 40, the current flowing through transistor switch 30 may be automatically limited to a safe and predetermined value. It is to be specifically understood, however, that with other applications, a single diode may housed. in place of the series-connected pairs 38 and 40 or,-with other applications, more than two diodes may be required, depending upon the circuit requirements.

From this description, it is apparent that a reliable, inexpensive and simple ignition system having the two very desirable high primary winding energizing current build-up and current limiting features, is provided.

In this specification, a type NPN transistor was set forth as the semiconductor switching device. It is to be: specifically understood that alternate switching devices having similar electrical characteristics or a type PNP transistor may be substituted therefor without departing from the spirit of the invention.

While a preferred embodiment of the present invention has been shown and described, it will be obvious to those skilled in the art that various modifications and substitutions may be made without departing from the spirit of the invention which is to be limited only within the scope of the appended claims.

What is claimed is as follows:

1. An ignition system for internal combustion engines comprising in combination, a pair of ignition breaker points which are opened and closed in timed relationship with the engine; an ignition coil having primary and secondary windings; a semiconductor switching device having two current carrying electrodes and a control electrode; a first resistor; a first series circuit including at least said primary winding of said ignition coil, said current carrying electrodes of said semiconductor switching device and said first resistor adapted to be connected across a source of direct current potential; an inductor; a second series circuit including at least said ignition breaker points and said inductor connected in parallel with said first series circuit; means for connecting said control electrode of said semiconductor switching device to a point between said ignition breaker points and said inductor whereby said inductor is connected across said control electrode and one of said current carrying electrodes of said semiconductor switching device for extinguishing said device when said breaker points open; a second resistor; means for connecting said second resistor in parallel with said ignition breaker points for rendering said device reconductive before said breaker points reclose; at least one semiconductor device and means for connecting said semiconductor device across the said control electrode of said semiconductor switching device and said first resistor, the ohmic value of said first resistor being selected to be of a value which, with rated current flow through said semiconductor switching device, will produce a potential drop substantially equal to the potential drop across said semiconductor device whereby current flow through said semiconductor switching device is limited.

2. An ignition system for internal combustion engines comprising in combination, a pair of ignition breaker points which are opened and closed in timed relationship with the engine; an ignition coil having primary and secondary windings; at least one spark discharge device connected across said secondary winding; a normally conducting semiconductor switching device having two current carrying electrodes and a control electrode; a first resistor; a diode; a first series circuit including at least said diode; said primary winding of said ignition coil, said current carrying electrodes of said semiconductor switching device and said first resistor adapted to be connected across a source of direct current potential; an inductor; a second series circuit including at least said ignition breaker points and said inductor connected in parallel with said first series circuit; means for connecting said control electrode of said semiconductor switching device to a point between said ignition breaker points and said inductor whereby said inductor is connected across said control electrode and one of said current carrying electrodes of said semiconductor switching device for extinguishing said device when said breaker points open; a second resistor; means for connecting said second resistor in parallel with said ignition breaker points for rendering said device reconductive before said breaker points reclose; at least one semiconductor device and means for connecting said semiconductor device across the said control electrode of said semiconductor switching device and said first resistor, the ohmic value of said first resistor being selected to be of a value which, with rated current flow through said semiconductor switching device, will produce a potential drop substantially equal to the potential drop across said semiconductor device whereby current flow through said semiconductor switching device is limited.

3. An ignition system for internal combustion engines comprising in combination, a pair of ignition breaker points which are opened and closed in timed relationship with the engine; an ignition coil having primary and secondary windings; at least one spark discharge device connected across said secondary winding; a normally conducting transistor switching device having base, emitter and collector electrodes; a first resistor; a diode; a first series circuit including at least said diode, said primary winding of said ignition coil, said collector-emitter electrodes of said transistor switching device and said first resistor adapted to be connected across a source of direct current potential in that order; an inductor; a second series circuit including at least said ignition breaker points and said inductor connected in parallel with said first series circuit; means for connecting said base electrode of said transistor switching device to a point between said ignition breaker points and said inductor whereby said inductor is connected across said base-emitter electrodes of said transistor switching device for extinguishing said device when said breaker points open; a second resistor; means for connecting said second resistor in parallel with said ignition breaker points for rendering said transistor switching device reconductive before said breaker points reclose; at least one semiconductor device and means for connecting said semiconductor device across the said base electrode of said transistor switching device and said first resistor; the ohmic value of said first resistor being selected to be of a value which, with rated current flow through said transistor switching device, will produce a potential drop substantially equal to the potential drop across said semiconductor device whereby current flow through said transistor switching device is limited.

References Cited UNITED STATES PATENTS 2,955,248 10/1960 Short 123-148 X 3,213,320 10/1965 Worrell. 3,285,234 11/1966 McLaughlin 123-148 3,288,125 11/1966 Guyton 123148 RALPH D. BLAKESLEE, Primary Examiner. 

